Siobhan Fallon (and her many aliases) is an American actress and writer.
A documentation is useful.

Documentation:
IMDb
Wikipedia

From CLT:
Siobhan Fallon
Siobhan Fallon Hogan (49/321)
Siobhan J. Fallon (2/76)
Siobhan Fallon-Hogan (1/1)
Siobahn Fallon (1/10)




Siobhan Fallon (4 unconfirmed)

A Cool, Dry Place
All We Had
Another Happy Day
Boiler Room
Charlotte's Web
Daddy Day Care
Dancer in the Dark
Dogville
Fever Pitch
Fool Rush In
Forrest Gump
Funny Games (2007)
Going in Style
Greedy
Holes (2003)
Law & Order: SVU: S04E25
Jury Duty
Krippendorf's Tribe
Men In Black
Only You (1994)
Saturday Night Live: The Best of Jerry Seinfeld
Seinfeld: S02E09
Seinfeld: S03E02
Seinfeld: S05E21
Someday this pain will be useful to you
Striptease
The Bounty Hunter (2010)
The Golden Girls: S06E07
The Negotiator
The Paper
The Photographer (2002)
Third Watch: S01E22
What's the worst that could happen?

Siobhan Fallon Hogan (5 unconfirmed)

30 Rock: S01E17
Another Happy Day
Baby Mama
Big Trouble
Charlotte's Web
Daddy Day Care
Dogville
Fever Pitch
Forrest Gump
Fred: The Movie
Fred 2: Night of the Living Fred
Funny Games (2007)
Going in Style
Holes (2003)
I'll Believe You
Law & Order: SVU: S04E25
MacGyver: S01E14
Men In Black
Scorpion: S03E04,05,06
Someday this pain will be useful to you
New in Town (2009)
Rescue Me: S01E03,09,11
The Bounty Hunter (2010)
The Negotiator
The Paper
Wayward Pines: S01E01,02,03,04,08,09,10
We need to talk about Kevin

Siobhan J. Fallon (0 unconfirmed)

Forrest Gump

Siobhan Fallon-Hogan (1 unconfirmed)

Rain (2001)

Siobahn Fallon (0 unconfirmed)

The Negotiator










Siobhan Fallon (19 confirmed)

A Cool, Dry Place confirmed by T!M
All We Had confirmed by Mad Rockatansky
Boiler Room confirmed by Mad Rockatansky
Dancer in the Dark confirmed by AiAustria
Fools Rush In confirmed by T!M
Greedy confirmed by T!M
Jury Duty confirmed by AiAustria
Men In Black confirmed by AiAustria
Only You confirmed by T!M
Saturday Night Live: The Best of Phil Hartman confirmed by huskersports
Seinfeld: S02E09 confirmed by T!M
Seinfeld: S03E02 confirmed by T!M
Seinfeld: S05E21 confirmed by T!M
Someday this pain will be useful to you confirmed by Mad Rockatansky
Striptease confirmed by Mad Rockatansky
The Negotiator confirmed by AiAustria
The Paper confirmed by T!M
What's the Worst That Could Happen? confirmed by T!M
We need to talk about Kevin confirmed by AiAustria

Siobhan Fallon Hogan (16 confirmed)

30 Rock: S01E17 confirmed by T!M
Another Happy Day confirmed by AiAustria
Baby Mama confirmed by T!M
Big Trouble confirmed by T!M
Charlotte's Web confirmed by T!M
Daddy Day Care confirmed by T!M
Dogville confirmed by AiAustria
Fever Pitch confirmed by AiAustria
Fred: The Movie confirmed by Mad Rockatansky
Fred 2: Night of the Living Fred confirmed by Mad Rockatansky
Funny Games confirmed by AiAustria
Going in Style confirmed by T!M
Holes (2003) confirmed by Mad Rockatansky
Law & Order: SVU: S04E25 confirmed by AiAustria
New in Town confirmed by T!M
The Bounty Hunter confirmed by T!M

Siobhan J. Fallon (1 confirmed)

Forrest Gump confirmed by AiAustria

Wayward Pines: S01E01,02,03,04,08,09,10 - Siobhan Fallon Hogan as Arlene Moran

The Golden Girls: S06E07 as Siobhan Fallon (Abby)

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I'll Believe You as Siobhan Fallon Hogan (Larry Jean)

Third Watch: S01E22@0:44:37
SIOBHAN FALLON    ANNETTE

The house that Jack built (2018) as Siobhan Fallon Hogan

'MacGyver: Season 1': Siobhan Fallon Hogan

A new variant.

The Professor --> Siobahn Fallon Hogan as Donna

Quoting T!M:

Quote:
So the common name has shifted: with 24 titles vs. 21 confirmed titles and not enough unconfirmed titles left to affect that balance, it's now Siobhan Fallon Hogan.

At least three titles missing:
The Photographer (2002)
Scorpion: S03E04,05,06
Rain (2001)

... but let's wait for the next thread update...